JPH08272222A - Transfer belt device - Google Patents

Abstract

PURPOSE: To prevent the soaring up of toner from a photoreceptor surface caused before a transfer, in the case of transferring a toner image from a transfer belt to a recording paper. CONSTITUTION: This transfer belt device is constituted so that a holding roller 32 on which the transfer belt 31 is extended and which is located on the upstream side of carrying is energized to the peripheral side of a photoreceptor drum 10 by a compression spring 30c, to bring the wound transfer belt 31 into contact with a drum surface and prevent a very small gap from appearing between a belt surface and the drum surface on the upstream side of a nip part 35 and a voltage having the same polarity as that of the toner image on the drum is applied from bias supply HV1 to the holding roller, at the same time when a voltage having a polarity opposite to that of the toner is applied from transfer power supply HV2 to the transfer wire 36a of a corona discharger 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device for transferring a toner image on an image carrier to a recording material, which is used in an electrostatic recording type image forming apparatus, and more particularly to transfer of a toner image by a belt and recording material. The present invention relates to a transfer belt device that conveys paper.

[0002]

2. Description of the Related Art As a means for transferring a toner image formed on an image bearing member to a recording material, a so-called transfer using a transfer belt is used because a transfer area is wide and a stable transfer performance and a recording material conveying function can be obtained. A belt device is used.

In the above-mentioned transfer belt, the belt surface stretched between rollers is pressed against the peripheral surface of the image carrier to form a nip portion,
A transfer electrode is formed inside the belt corresponding to the nip portion to form a transfer area, and the recording material is sandwiched in the transfer area by rotating the transfer belt in synchronization with the peripheral speed of the image carrier. The toner image is transferred while being attached and conveyed.

[0004]

However, in the case of transfer using such a transfer belt, just before the recording material enters the nip portion, a part of the toner on the image carrier is transferred to the recording material side prior to the transfer. There is a problem of flying and causing a phenomenon of so-called character dust to cause image blurring. Further, there is a transfer failure (so-called transfer repelling) due to the toner being charged to the opposite polarity due to the gap discharge generated between the recording material and the image carrier, and the transfer current is transferred in order to transfer a large amount of toner. If the relative humidity increases to 70% or more even under the same transfer current, the image quality tends to deteriorate.

A great change can be seen in the generation state of these depending on the paper quality of the transfer material. On the other hand, if the transfer current is lowered, there is a tendency that a transfer failure (poor transfer) that cannot be sufficiently transferred easily occurs, and under a wide range of environmental conditions, transfer cissing, transfer blurring, and poor transfer of various transfer materials may occur. Determining a transfer condition that does not occur is a difficult problem even if a process control based on a humidity sensor or a transfer material information signal is adopted.

This tendency is particularly remarkable in a transfer apparatus used in a color image forming apparatus of a type in which toner images of a plurality of colors are superposed on an image carrier and then transferred to a recording material at once. A transfer electric field more than twice the above is required, and the allowable region where the above problems do not occur is further narrowed.
Further, due to changes in the environment, paper quality, etc., this permissible range is greatly shifted and becomes more unstable. In particular, under high humidity conditions, it may not be possible to find a transfer current condition that provides vivid color image quality in which both transfer repellency and poor transfer do not occur even on normal paper.

The present invention solves this problem and improves the result.
A transfer belt capable of preventing image blurring and transfer repelling in the transfer belt device and transferring a high-quality color image onto a recording material without damaging the color tone even when transferring a toner image formed by superposition. The purpose is to provide a device.

[0008]

SUMMARY OF THE INVENTION The above-mentioned object is to provide a transfer belt device for transferring a toner image on an image carrier to a recording material and transporting the toner image, from the upstream side to the inside of the belt facing the image carrier. An electrode and a second electrode are provided so as to intersect with each other in the moving direction of the belt, an electric charge having the same polarity as that of the toner is applied to the first electrode, and the second electrode is opposite to the toner with respect to the belt. This is achieved by a transfer belt device characterized in that a charge for applying a polar potential is applied.

[0009]

When the toner image on the photoconductor drum 10A is transferred to the recording paper P by the transfer belt device 30A composed of the transfer belt 31A and the corona discharger 36A arranged inside the transfer belt 31A as shown in FIG. As shown in FIG. 5, the degree of character dust (which causes image blurring) on the formed image is relatively small (1.5 mg / cm ² or less) of the toner adhesion amount.
There are few letters in the ranking, and the rank showing the evaluation level is 3
As described above, a transferred image with good image quality can be obtained, whereas when the amount of toner adhered increases (1.5 mg / m ² or more), the rank becomes 3 or less and the image quality deteriorates (Bad). There is a tendency.

However, also in the above-mentioned transfer belt device 30A, the roller 32 on the entrance side of the recording paper P when transferring the toner image.
When the voltage V _PR having the same polarity as that of the toner is applied to A, it is possible to prevent the toner of the toner image on the drum side from flying to the recording paper P side and suppress the occurrence of character dust. As an example, when the voltage applied to the roller 32A is V _PR = −900V, the character dust rank is 4 or more even if the toner adhesion amount is increased to 2.5 mg / cm ² , and the image blurring is almost eliminated. If the toner adhesion amount of 2.0 mg / cm ² is a good toner image, V _PR
= 3 for character dust that is practically acceptable even at -600V
It was confirmed that the level could be suppressed to the above level.

Prior to the transfer of the recording paper P, the potential of the photosensitive member in the area having the toner image on the drum is lowered in advance by the pre-transfer image exposure means for exposing corresponding to the portion where the toner image is attached. It was also possible to confirm that the degree of character dust can be further improved by leaving it. This is because the photoconductor potential of the area having the toner image is lowered by pre-transfer image exposure,
It is considered that the flying electric field of the toner was lowered.

FIG. 6 shows the difference in character dust rank depending on the presence or absence of pre-transfer image exposure when the voltage V _PR is not applied to the roller 32A and when V _PR = -600 V having the same polarity as the toner is applied. It is recognized that the rank is further improved in the arrow direction in any case by performing the pre-transfer image exposure.

From the above, the phenomenon of character dust occurring when the toner image is transferred is that the potential difference between the potential of the toner image portion on the drum and the voltage V _PR applied to the roller 32A causes the character dust. Are closely related to each other. Therefore, by making the voltage V _PR equal to the surface potential of the toner image portion on the drum, or by setting the voltage having a high absolute value on the same polarity side as the toner, the character dust is generated. It has become clear that the occurrence of can be greatly improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments, the structure and operation of an image forming apparatus having a transfer belt device will be described.

FIG. 1 is a sectional view showing the construction of a color image forming apparatus as an embodiment of the image forming apparatus.

In the figure, reference numeral 10 denotes a photosensitive drum which is an image bearing member, which is formed by coating an OPC photosensitive layer on the drum and is grounded and driven and rotated clockwise. Reference numeral 12 denotes a scorotron charger, which applies a uniform charge of V _{H to} the peripheral surface of the photosensitive drum 10 to V _G.
It is given by a corona discharge with a grid and a corona discharge wire that are held at a potential. This scorotron charger
Prior to charging by 12, the PCL 11 using a light emitting diode or the like is exposed to eliminate the history of the photoconductor until the previous printing, and the peripheral surface of the photoconductor is neutralized.

After the photosensitive member is uniformly charged, the image exposure means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 denotes a polygon mirror 131 that rotates using a laser diode (not shown) as a light emitting source, and a reflection mirror 13 via an fθ lens and the like.
The optical path is bent by 2 for scanning, and a latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10.
In this embodiment, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L.

Yellow (Y) on the periphery of the photosensitive drum 10,
Developers each containing a developer composed of toner such as magenta (M), cyan (C), black (K), and a carrier.
14 is provided, and first, the development of the first color is performed by the developing sleeve 141 which contains a magnet and holds the developer and rotates. The developer is a carrier in which a ferrite core is coated with an insulating resin around it, a polyester as a main material, a pigment according to the color, and a charge control agent,
It consists of toner to which silica, titanium oxide, etc. have been added.
The layer is regulated to a layer thickness of ~ 600μm and transported to the development zone.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.4 to larger than the layer thickness (developer).
As 1.0mm, V _AC AC ice and V _DC D
The C bias is superimposed and applied. Since V _DC and V _H and the toner are charged with the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion, which has a higher potential than V _{DC, and} has a potential higher than V _DC. attached to a lower V _L portion of visualized (reversal development) is carried out.

After the visualization of the first color is completed, the process for forming the image of the second color is started, the uniform charging is performed again by the scorotron charger 12, and a latent image based on the image data of the second color is formed by the image exposing means 13. To be done. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M ′ and V _M ′. In the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
When the latent image of is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M > V
_It may be an intermediate potential that becomes _L.

An image forming process similar to that for the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, the recording paper P fed from the paper feeding cassette 21 by the paper feeding mechanism 22 is the transfer belt 31 according to the present invention.
The multi-color image on the peripheral surface of the photoconductor drum 10 is fed all at once to the recording paper P by the transfer belt device 30 which is stretched.
Moved to the top.

The transfer belt device 30 according to the present invention has the structure shown in FIG. The transfer belt 31 used in the transfer belt device 30 has a FLC layer formed on the outside of a urethane rubber substrate and has a volume resistivity of 10 ¹⁰ to 10 ¹¹ Ω · cm and a thickness of 0.61 m.
Endless rubber belt with m and circumference of 52 cm, holding roller 32
It is stretched between 33 and 33 and is used at an extension rate of 3% by the bias of the tension roller 38.

The holding rollers 32 and 33 and the tension roller 38 are supported by an inner frame 30b which is housed in an outer frame 30a of the transfer belt device 30, and are compressed by a compression spring 30c with a shaft 33a of the holding roller 33 as a fulcrum. It is biased clockwise.

At the time of transfer, the holding roller 32 is wound around the transfer belt 31 by abutting rollers (not shown) provided at both ends contacting the non-image area on the side edge of the photosensitive drum 10.
And a roller having an outer diameter of φ12 mm that regulates the clearance between the photosensitive drum 10 and the peripheral surface of the photoconductor drum 10 and the contact state to a predetermined value, and is rotated by the conveyance of the belt.

On the other hand, the holding roller 33 is connected to the power system of the main body of the apparatus and is driven to rotate in the counterclockwise direction.
It is a roller of 5.3 mm, and has a surface roughness of Rmax 55 to 85 μm, so that it reliably circulates in the counterclockwise direction without slipping with the transfer belt 31, and the transfer belt 31 is synchronized with the peripheral speed of the photosensitive drum 10. And then transport.

In the transfer belt 31, the belt surface between the holding roller 32 corresponding to the first electrode and the holding roller 33 is brought into pressure contact with the peripheral surface of the photosensitive drum 10 to form a nip portion 35, which is opposed thereto. The corona discharger 36 corresponding to the second electrode is arranged inside the belt to form a transfer area where the toner image is transferred.

The corona discharger 36 is composed of a transfer wire 36a made of WO ₃ and having a diameter φ0.08, and an electrode plate 36b made of SUS304 with a side plate distance of 7.5 mm. The transfer wire 36a is arranged to face the drum surface with a distance of 7 mm.

Further, the holding roller 32 is a transfer belt 31 which is wound by setting the outer diameter of the abutting roller.
The outer circumference of the drum is in contact with the drum surface so that no gap is formed on the drum surface.

When the toner image is transferred, the transfer wire 36a of the corona discharger 36 is supplied with a variable voltage in the range of +3.5 to +9.0 kV, which has the opposite polarity to the toner, by the transfer electrode power supply HV2 which is the second electrode. Is applied to the shaft 32 of the holding roller 32.
A variable voltage V _{PR in} the range of 0 to −1500 V having the same polarity as the toner is applied to a by the bias power supply HV1 which is the first electrode, and the holding roller 32 is used as a pre-transfer roller before corona discharge.

Next, the recording paper P and the transfer belt 31 which conveys the recording paper P are biased by a bias power supply H to the above-mentioned holding roller 32.
By applying a voltage of a negative potential from V1, a charge having the same polarity as that of the toner is applied to prevent air discharge to the recording paper P side, the toner is prevented from flying, and the above-described transfer bleeding and character dust cause image blurring. Occurrence is avoided.

Further, since the transfer belt 31 is in contact with the drum surface over the entire area from the downstream side of the holding roller 32 to the nip portion 35, after the potential is applied to the holding roller 32, the recording paper P is directed toward the downstream side. Even if a positive electric field is gradually formed on the surface, gap discharge, that is, air discharge does not occur, so that the phenomenon of so-called transfer cissing is also avoided.

It should be noted that although a minute gap is formed on the upstream side of the holding roller 32 that is in pressure contact with the photosensitive drum 10, the recording paper P and the transfer belt 31 are applied with a negative potential by the holding roller 32, so that recording is performed. Even if the resistance of the paper P is drastically reduced, the positive charge transmitted through the recording paper or the transfer belt flows into the holding roller 32, that is, is neutralized by the negative charge from the holding roller 32, and the small gap is generated. The gap potential is suppressed to a small level, so that transfer cissing does not occur.

When the occurrence of transfer cissing was confirmed by the transfer belt device 30 under the following process conditions, the results shown in the graph of FIG. 3 were obtained.

As the process conditions, the conveying speed of the recording paper P is 74 mm / sec, the charging potential of the photosensitive drum 10 is -650 V, and the toner adhesion amount of the cyan toner image superimposed on the magenta toner image is 2.0 mg / The two-color superposed image of cm ² is recharged to around −650 V when passing through the scorotron charging 12, and then reaches the transfer pole.

As the recording paper P, a 20-pound copy paper left for 24 hours or more in an environment of temperature 30 ° C. and humidity 70% RH or more was used, and the machine body was also tested under the same environmental conditions for 8 hours or more. Was carried out.

The result is that the bias voltage applied to the holding roller 32 and the transfer belt 31 at the pressure contact portion of the holding roller 32.
When the occurrence status of the phenomenon of transfer cissing was investigated using the gap between the photosensitive drum 10 and the peripheral surface of the photosensitive drum 10 as a parameter,
When a charging potential of the photosensitive drum 10, that is, a potential of −900 V higher than the potential of the toner image is applied to the holding roller 32, the evaluation rank is improved, the degree of transfer cissing is reduced, and the gap described above is set to 0. The effect is greatest when the transfer belt 31 and the drum surface are in contact with each other, and even if the transfer voltage applied to the transfer wire 36a is high, the rank is 4 or more, and the transfer repelling is suppressed to a practically unimpeded level. It was confirmed that

The recording paper P separated from the photosensitive drum 10 is
The shaft 33a of the holding roller 33 on the downstream side which stretches the transfer belt 31.
Transfer belt 31 after receiving static electricity by AC corona discharge with the counter electrode as the counter electrode, or while receiving AC corona discharge.
Separate from. A cleaning blade 37 removes the toner attached to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is separated from the photosensitive drum 10 about a shaft 33a of a holding roller 33 on the downstream side as a rotation center during the formation of a multicolor image.

The recording paper P holding the multicolor image separated from the transfer belt device 30 is conveyed to a fixing device 23 composed of two pressure-bonding rollers having a heater inside at least one roller, and is transferred between the pressure-bonding rollers. The applied toner is melted by applying heat and pressure, fixed on the recording paper P, and then discharged to the outside of the apparatus.

After the transfer, the residual toner remaining on the peripheral surface of the photosensitive drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, and then is removed from a rubber material which is in a cleaning device 16 and abuts on the photosensitive body. It is scraped off into the cleaning device 16 by the cleaning blade 16a, discharged by a screw or the like, and then stored in the recovery box. It should be noted that the above-mentioned static eliminator 15 can also serve as static eliminator of the recording paper depending on the arrangement.

The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 16 is exposed by the PCL 11 and then uniformly charged by the scorotron charger 12.
Enter the next image forming cycle. The cleaning blade 16a is separated from the surface of the photoconductor during the formation of the multicolor image,
AC neutralization by 15 is kept in OFF state.

[0043]

According to the present invention, the toner is prevented from flying from the surface of the photosensitive member in the initial stage of image transfer, so that the occurrence of so-called character dust and image blurring can be avoided, and as a result, the recording paper can be printed even in a high humidity environment. On the other hand, a transfer belt device capable of transferring a clear color image having a color tone without transfer cissing is provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus including a transfer belt device of the present invention.

FIG. 2 is a cross-sectional configuration diagram showing a transfer belt device of the present invention.

FIG. 3 is a graph showing the effect of the present invention on transfer cissing in the transfer belt device related to the present invention.

FIG. 4 is a cross-sectional configuration diagram showing a conventional transfer belt device.

FIG. 5 is a graph (No. 1) showing the effect of the present invention on the character dust in the transfer belt device related to the present invention.

FIG. 6 is a graph (No. 2) showing the effect of the present invention on the character dust in the transfer belt device related to the present invention.

[Explanation of symbols]

 10 photoconductor drum 30 transfer belt device 30a outer frame 30b inner frame 30C compression spring 31 transfer belt 32, 33 holding rollers 32a, 33a (roller) shaft 35 nip 36 corona discharger 36a transfer wire 36b electrode plate

Claims (2)

[Claims] 1. A transfer belt device for transferring a toner image on an image carrier to a recording material and transporting the toner image, wherein a first electrode and a second electrode are provided from the upstream side inside a belt facing the image carrier. The second electrode is provided so as to intersect with the moving direction of the belt, and a charge having the same polarity as the toner is applied to the first electrode,
A transfer belt device, wherein an electric charge for applying a potential having a polarity opposite to that of the toner is applied to the electrode of the transfer belt. 2. The transfer belt device according to claim 1, wherein the first electrode is in contact with the image carrier with the belt interposed therebetween.